@Sci_Fi_Rulez: didn't realise you mentioned 'at full power', in which case Katara stomps alone because of bloodbending. The physics are different to telepathy so Magneto gets ultra brutally raped. Without bloodbending though, even with both at full power, Magneto stomps in an unholy manner.

We aren't sure what he is currently capable of but OP listed at full strength.

Magneto at his strongest can open wormholes and manipulate molecules. There are to many factors against bloodbending even being viable, even at her strongest it still needs a full moon, even if there is one he has accelerated mental processes along with thought based activation so not only can he activate his powers faster and more easily he could also activate them under the influence of bloodbending.

1) Katara could only blood bend during the full moon, and there is only evidence of her doing it once.

2) Magneto can control the iron in blood. In theory he can counter her blood bending this way.

3) It would be suuuuuuper out of character for Katara to blood bend anyone.

4) Even if Katara did blood bend Magneto he can still use his powers without moving, meaning he can take her out any number of ways (use the iron in her blood to tear her apart, stop the flow of blood to her brain, impale her with any of the various metal items that one would find in San Fransico...)